1. Technical Field
The present disclosure relates to a positive electrode for a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery.
2. Description of the Related Art
A positive electrode for a nonaqueous electrolyte secondary battery (hereinafter, simply referred to as “positive electrode”) includes a positive electrode current collector and a positive electrode mixture layer on the current collector. The positive electrode has a portion serving as a lead to be electrically connected to, for example, a positive electrode terminal, and the portion includes an exposed portion where the positive electrode mixture layer is not formed to expose the surface of the current collector. In order to secure smooth movement of lithium ions between positive and negative electrodes, the positive electrode is designed to be smaller than the negative electrode. In such a case, the exposed portion of the positive electrode current collector faces the negative electrode with a separator therebetween. If foreign matter enters between the exposed portion and the negative electrode and breaks through the separator, the exposed portion may come into contact with the negative electrode to cause a low-resistance internal short-circuit, which generates a flow of a large current and thereby generates large heat.
In order to avoid such a low-resistance internal short-circuit, for example, Japanese Unexamined Patent Application Publication No. 2013-45659 discloses a positive electrode including an insulating layer formed by applying a binder solution containing a binder resin and a solvent to the exposed portion of a positive electrode current collector.
However, since the insulating layer disclosed in Japanese Unexamined Patent Application Publication No. 2013-45659 is a thin film layer made of only a binder resin, the effect of preventing an internal short-circuit due to contamination of foreign matter is low. In particular, if the size of foreign matter is large, it is inferred that the effect of the insulating layer preventing an internal short-circuit is insufficient.
In addition, a nonaqueous electrolyte secondary battery is required to reduce the quantity of heat due to an internal short-circuit caused between the area of the positive electrode mixture layer and the negative electrode by, for example, nail sticking. It is, however, difficult to reduce the quantity of heat by the technology disclosed in Japanese Unexamined Patent Application Publication No. 2013-45659.